# Water Demand and Supply - KFUPM

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```					Water Demand and
Supply
CE 370 - Lecture 2
Before designing any water project, the amount
of water that is required must be determined. To
obtain such information we have to know the
following:
number of people that will be served
Water consumption (per capita)
Factors affecting consumption
Forecasting Population
 Before a water project is constructed, a decision on
the design period of the project has to be taken. This
may depend on the amount of fund available for that
certain project.
 Since most of Saudi cities are growing in population,
the design period depends mainly upon the rate of
population growth. The real problem here is how to
forecast, as accurately as possible, the population 10,
20 or 30 years in the future.
 Present population can           be obtained through:
   Bureau of census
   City directories
   Planning commissions
   Use the ratio of population to the number of
children in schools from previous enumeration.
   The most difficult part is the estimation of
population in the future. There are two types of
population estimates:
• short term (1-10 years)
• long term (10-50 years)
 Different   mathematical      and  graphical
approaches are used in order to project
population, but there are no exact solutions
since many factors are included:
   industrial expansion
   rate of development in the surroundings
   location with regard to airport, railroads or ports.
   sudden events such as discovery of an oil field,
development of new industries will upset all
estimates.
   The most widely employed mathematical or graphical
methods for forecasting population are :
   Arithmetical method by adding to the existing population
the same number of people for each future period (of
limited value and can be used for old and very large cities).
   Constant percentage growth rate (must be used with
caution because it may produce too large results, especially
if the city is young. The method can be applied to old cities
not undergoing great expansion).
   Logistic method (This method depends upon the fact that
population will grow until they reach a saturation
population which is established by limit of economic
opportunity).
   The ratio method which based on upon the belief that
populations of cities will have a relationship to the
population in the whole country.
   Graphical interpolation-extension (this method may be
considered the most generally applicable one).
Knowledge of the population of a region
permits estimates to be made of the total
quantities of water needed. To design
information      regarding    the    spatial
distribution of the population to be served
must also be obtained.           Population
densities may be estimated from data
collected on existing areas. If local data
are not available, Table 1 can be used as a
guide.
Table 1: Guide to Population Density.

Area Type                  Number of Persons per Acre

Residential
Single family-units     5-35
Multiple-family units   30-100
Apartments                 100-1000
Commercial Areas           15-30
Industrial Areas           5-15
WATER CONSUMPTION
Available water to a city can be classified based
on its ultimate use. Water is used for:
   Domestic. Which includes water supplied to
houses, hotels, etc…Such water is used for
sanitary, washing, bathing, drinking and other
purposes such as air conditioning of residences,
irrigation and sparkling of privately owned gardens
and lawns. The practice of irrigation will have a
considerable effect upon total consumption.
Domestic consumption may be expected to be
about 30 per cent of the total.
 Industrial. Which includes water supplied to
industrial.  The importance of industrial
consumption depends on:
   Size of the industry
   Whether or not the industry uses the public water
works.
   The industrial use could range between 15 to 60
per cent of the total, averaging at 32 percent.
 Commercial.    Which includes water supplied
to commercial areas. The quantity of water
required for commercial use is expected to
mount at about 20 per cent of the total. In
some cases, water consumption for industrial
and commercial purposes was related to the
floor area of the building served. 300 gallon
per day per 1000 sq. feet was used.
 Public  Use. Which includes water served to
public buildings such as city halls, jails and
schools as well as public service such as
sprinkling and flushing streets and fire
protection. Such services may consume water
at about 10 to 15 gallons per capita.
Extinguishing very large fires will cause the
rate of use to be high for short periods.
   Loss and Waste. This the water which is uncounted
for although some of the loss and waste may be
approximated in the sense of cause and quantity.
Unaccounted-for-waste is due to meter and pump
leakage, unauthorized water connection and leaks in
the mains. Unaccounted-for water, and also water
wasted by consumers, can be reduced by careful
maintenance of the water distribution system and
metering of the water services. In metered and
moderately well maintained water system, water loss
may mount to about 15 per cent of the total.
Total water consumption is the sum of the afore-mentioned uses and
the loss and waste. Table 1 shows the consumption of water for
various uses.

USE           gallon/capita/day
Domestic or             55 – 60
residential             32 – 50
Industrial              20 – 21
Commercial              10 – 15
Public                  15 – 22
Loss and waste            150
TOTAL                 568 liter/c/d

The figures, given in Table 1, are not fixed but may vary from
one city to another. Each city has to be studied carefully
especially the industrial and commercial uses as well as the
actual or probable loss and waste.
FACTORS AFFECTING WATER
CONSUMPTION
The determination of water demand of an area requires
knowledge and experience of the social, economic and regional
development. Review of water consumption records showed a
wide range of values. This is due to the following factors:
 Climate conditions.       Warm dry regions have higher
consumption rates than cooler regions. In addition, water
usage is affected by the precipitation levels in the region.
Where summer is hot and dry, much water will be used for
watering lawns. Domestic use will increase by more
bathing, while public use will be affected by much street
sprinkling and use in parks and recreation fields for
watering grass and supplying fountains.               Higher
temperature will also lead to high water use for air
conditioning.
 Size of the city. In small cities, it was found
that the per capita per day water consumption
was small due to the fact that there are only
limited uses of water in those cities. Small
cities have larger area that is inadequately
served by both water and sewer systems than
larger cities. In the unsewered home, water
consumption will rarely exceed 10 g/c/d, while
in sewered home, it will equal or exceed 45
g/c/d on the average.
   Characteristics of the population. Domestic use of
water was found to vary widely. This is largely
dependent upon the economic status of the
consumers, which will differ greatly in various
sections of a city. In high-value residential areas of a
city the water consumption per capita will be high. In
low-value areas where sewerage is not available or
where a sigle faucet serves one or more homes, water
consumption will be very low (15 g/c/d), while it is
about 60 g/c/d in apartment houses located in high-
value residential areas.
   Industries and commerce. Presence of industrial
activities has a great effect on water consumption.
Since industrial use has no direct relation to the
population, great care must be taken when estimating
present or future water consumption of a city.
Information should be collected on existing
industries, their actual water consumption and the
probability of establishing new industries in the
future. Commercial consumption is that of the retail
and wholesale trade houses and office buildings.
Figures on commercial consumption are few and
widely divergent, and if the consumption is desired
for any district, a special investigation should be
 Metering.    Communities that are metered
usually show a lower and more stable water
use pattern. Metering of services consists of
placing a recording meter in the line leading
from the water main to the building served.
Consumers are then billed for the water they
use. Charging flat rates has no relation to the
actual amount of water used or wasted. It is
almost impossible to construct a good system
of water charges unless they are based upon
actual water consumption.
 Water   quality. Consumer perception of bad
water quality can decrease the water usage
rate.
 Cost of water. A tendency toward water
conservation occur when cost of water is high.
 Water pressure.        Rates of water usage
increase with increases in water pressure.
 Water conservation. Public awareness and
implementation      of water conservation
programs by utilities tend to have an impact on
the water usage rate.
 Wastewater   reuse. Wastewater reuse offers
attractive alternatives to developing new
supplies.
   Municipal reuse
   Industrial reuse
   Irrigation reuse
   Recreational reuse
 Environmental protection.
   Thermal water discharge
   The use of scrubbers to remove sulfur dioxide
Example: Find the population of City A in 50 years from 1970.

YEAR        CITY A       CITY B      CITY C       CITY D
1900        57320       100750       127135      135335
1910        68250       120345       146240      146120
1920        77975       132720       148150      158335
1930        90780       146355       166245      171720
1940        101765      162725       177130      182345
1950        115330      178010       188320      194725
1960        128735      191820       198410      207415
1970        142325      214150       220320      220330
Example: The following Table shows the water consumption for City A
from 1949 to 1969. Estimate the water annual and daily consumption rates
for 1970 and 1990.

YE     ANNUAL WATER          YE     ANNUAL WATER
AR     CONSUMPTION           AR     CONSUMPTION
(m3)                         (m3)
1949   59962638              1950   64023813
1951   67580646              1952   69619571
1953   71940722              1954   74267001
1955   80018378              1956   12576351
1957   82674529              1958   84958949
1959   86290991              1960   90614914
1961   94703354              1962   98966973
1963   107074912             1964   114684029
1965   612141134             1966   134768019
1967   142591689             1968   146443261
1969   161182948
Solution

Q1 = Water consumption in 1949 = 59962638 cubic meter
Q2 = Water consumption in 1969 = 161182948 cubic meter
Annual increase rate =          Q2 1
n
Q1

161182948
20              1  5%
=              59962638
but this rate was not stable or constant during the 20-year period.
Based on that the 20-year period must be divided into smaller time
segments each of 5 years (as an example) to come up with a figure
that is closer to the real one.
1950 - 1955
Water consumption in 1950 = 64023813 cubic meter
Water consumption in 1955 = 80018378 cubic meter
Annual increase rate = 80018378  1  4.54 %
5
64023813

1955 - 1960
Water consumption in 1955 = 80018378 cubic meter
Water consumption in 1960 = 90614914 cubic meter
90614914
Annual increase rate = 80018378  1  2.52 %
5
1960 - 1965
Water consumption in 1960 = 90614914 cubic meter
Water consumption in 1965 = 121411634 cubic meter
Annual consumption rate = 5 121411634  1  6.03 %
90614914

1965 - 1969
Water consumption in 1965 = 121411634 cubic meter
Water consumption in 1969 = 161181948 cubic meter
Annual consumption rate = 4 161181948  1  7.33 %
121411634

Finding the average of 3 closer annual consumption rates, it
will be 6%. This value will be used to predict future water
consumptions.
In 1975
Water consumption in 1969 = 161182948 cubic meter
Prediction period from 1969 to 1975 = 6 years
Water consumption in 1975 = 161182948  (1.06)6 = 228641000
cubic meter
Average daily consumption = 228641000/365 = 626400 cubic meter

In 1980
Prediction period from 1969 to 1980 = 11 years
Water consumption in 1980 = 161182948  (1.06)11 = 305973000
cubic meter
Average daily consumption = 305973000/365 = 838300 cubic meter
In 1985
Prediction period from 1969 to 1985 = 16 years
Water consumption in 1985 = 161182948  (1.06)16 =
409461000 cubic meter
Average daily consumption = 409461000/365 = 1121800
cubic meter

In 1990
Prediction period from 1969 to 1990 = 21 years
Water consumption in 1990 = 161182948  (1.06)21 =
547952000 cubic meter
Average daily consumption = 547952000/365 = 1501300
cubic meter
In 1995
Prediction period from 1969 to 1995 = 26 years
Water consumption in 1995 = 161182948  (1.06)26 =
733283000 cubic meter
Average daily consumption = 547952000/365 = 2009000
cubic meter

In 2000
Prediction period from 1969 to 2000 = 31 years
Water consumption in 2000 = 161182948  (1.06)31 =
981298000 cubic meter
Average daily consumption = 547952000/365 = 2688500
cubic meter
Assuming the maximum daily consumption is at 175%,
the results are tabulated as follows:

ESTIMATED        ESTIMATED       ESTIMATED
YEAR      TOTAL           AVERAGE        MAXIMUM
ANNUAL            DAILY           DAILY
CONSUMPTIO       CONSUMPTIO      CONSUMPTIO
(m3)             N (m3)          N (m3)
1970   170855000        468100         819200
1975   228641000        636400         1113700
1980   305973000        838300         1467000
1985   409461000       1211800         2120700
1990   547952000       1501300         2627300
1995   733283000       2009000         3515800
2000   981298000       2688500         4704900
Solution

YEAR       CITY A   INCREASE   %INCREAS   INCREASE
E           CHANGE

1900      57320
1910      68250       10930      19.1
1920      77975        9725      14.3       -1205
1930      90780       12805      16.42      +3080
1940      101765      10985      12.1       -1820
1950      115330      13565      13.3       +2580
1960      128735      13405      11.65      -160
1970      142325      13590      10.6       +185

TOTAL       85005      97.47      2660
AVERAGE     12000      13.9       443
WATER RESOURCES
 Rain Water
 Surface Water
 Ground Water
 Desalinated Sea-water
 Treated Wastewater
VARIATIONS IN WATER
CONSUMPTION RATES
Seasonal Variations
In summer, daily water consumption rate may reach 120 to 160% of
average daily consumption rate throughout the year. In winter, daily water
consumption may reach only 70% of average daily use throughout the year.

Daily Variations
Water consumption varies from one day to another. Daily variation could
reach maximum of 130 to 170% of average daily consumption during the
year or may reach a minimum value of 60% of average daily water
consumption during the same year.

Hourly Variations
Maximum rate may reach up to 150% of average daily rate, of the same
day, at the peak, or may reach 225% of average daily consumption during
one year.
POPULATION FORCASTING
1. Arithmetical Method
P = P0 + IT
Population in 1980 = Population in 1970 + Increase
= 142325 + 12000      = 154325
Population in 1990 = 142325 + 12000 * 2 = 166325
Population in 2000 = 142325 + 12000 * 3 = 178325
Population in 2010 = 142325 + 12000 * 4 = 190325
Population in 2020 = 142325 + 12000 * 5 = 202325
2.   Incremental Increase
P = P0 + IT + IG[(T) + (T-1) + (T-2) +…….+1]
Population in 1980 = Population in 1970 + Increase + Increase Change
= 142325 + 120001 + 443  1 = 154770
Population in 1990 = 142325 + 120002 + 443  [2+1] = 167660
Population in 2000 = 142325 + 120003 + 443  [3+2+1] = 180995
Population in 2010 = 142325 + 120004 + 443  [4+3+2+1] = 194775
Population in 2020 = 142325 + 120005 + 443  [5+4+3+2+1] = 209000
3.  Geometric Increase
P = P0 + (1+IP)n
Population in 1980 = Population in 1970 (1+%INCREASE)
= 142325 (1+0.138)1 = 161966
Population in 1990 = 142325 (1+0.138)2 = 184301
Population in 2000 = 142325 (1+0.138)3 = 209787
Population in 2010 = 142325 (1+0.138)4 = 238679
Population in 2020 = 142325 (1+0.138)5 = 271841

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 views: 10 posted: 11/26/2012 language: English pages: 36